Apparatus for forming sheets from plastic material



J y 31, 5-v G. A. HOGGATT 2,380,527

I APPARATUS FOR FORMING SHEETS FRO M PLASTIC MATERIAL Filed Jar}. 2, 1943 mama July 31, 1 945 APPARATUS non romaine sm'rs mom rms'rrc. MATERIAL Gilbert A. Hoggatt, Winnetka, Ill assignor to Cartain-Teed Products Corporation,- Chicago, lit,- a corporation of Maryland Application January 2, 1948, Serial No. 471,118

2 Claims.

' This invention relates to a process of and apparatus for producing sheets or slabs formed of a core, between cover sheets, of material set or otherwise hardened from a plastic condition. In one-form such a product may be a structural element in which the core material is an hydraulic setting material in set condition, having adhering to the faces of the core cover sheets of initially flexible. material providing protection forv the core and which may act as tension members, the core acting as the stiilening or compression member. The invention is particularly concerned with the production of so-called gypsum wallboards in which the core is principally calcined gypsum in set condition and the cover sheets are of felted fibrous structure and may be in theiorm of paper of suitable thickness which may be made on a paper machine. r

In the manufacture of wallboards, such as gypsum'wallboards, having a hydraulic setting core material it is common practice to feed from a supply roll a continuous sheet of paper, ordinarily referred to as the bottom cover paper, supported to move horizontally in the plane of the extent oi the paper ,and continuously over a long distance in the wallboard machine. This distance of travel is required in order that the hydraulic setting material in plastic condition carried upon this cover paper may have time to set. The sec-- and cover paper, ordinarily referred to as the top cover paper, is applied upon the plastic core material and held by means of a so-called top forming roll in proper relation thereto so that when the core material is set the cover papers spaced apart by the core will have a strong bond with and provide the facing layers for the set core in the sheets or slabs.

In the conventional apparatus a bottom forming roll is commonly used placed vertically under the top formingroll and beneath the bottom cover paper to support this bottom cover paper and the core material carried thereby at the point of forming the board thickness. these two cover papers, as determined by the spacing of the two forming rolls, is intended to determine the thickness of the wallboard. As hereafter explained, it does not do so.

It is the general practice that the amount oi calcined gypsum, made plastic by mixture with water. which is delivered upon the bottom cove paper is so controlled that a mass of the plastic core materialbuilds up against the upper formin roll, that is, against the top cover paper in contact with this roll. This roll by its setting is intended to be eifective not only to position ini- The spacing oi tially the top cover paper at proper spacing from the bottom cover paper but also to crowd back and prevent from entering between the cover sheets, as they and the core material are moved forward, the excess of theplastic mass over that required to 1111 up the space between the cover sheets for the required thickness of the board. By properly distributing the core material over the width of the bottom cover paper. the top cover pa" per being fed with its edges in suitable lateral relation to the edges of the bottom cover paper. the space between the cover papers may be filled from one edge to the other as the papers are moved hetween the forming rolls. In the manufacture of some types of such gypsum wallboards the bottom cover paper after application of the core material C thereto is folded over upon the core material to form so-called "closed edges}? the top cover paper being delivered in such relation as to lap its edges upon the folded over margins oi the bottom cover paper and so that it may be adhesively bonded thereto by a suitable adhesive.

The accumulation of such a mass built up against the top cover paper is advantageous or necessary in the respect that within limits, var.- iations in the amount of the core material as it is delivered upon the bottom cover paper may occur without reducing the amount of core material avaliable to completely fill the space between the cover sheets as they pass beneath the forming rolls. It has been found in'practice, however, that variations in the thickness of the product nevertheless occur. To secure a desired thickness'it has been found necessary that the roll shall always be set somewhat closer together than the desired thickness to which the product is to be made. Variations in thickness, however, still may occur with variations in the consistency, plastic ity, or other physical properties of the plastic core material, in the amount thereof which is bein carried against and held back by the forming rolls, and in other conditions attendant on-the board formation.

Ihave observed in making the ordinary board products of this type that, immediately after the formed board has passed the forming rolls and is proceeding in the direction of its length, the top cover paper apparently is slightly lifted. that is to say, it does not proceed directly tangent to the upper forming roll and parallel to the move ment of the bottom cover paper but appears first to proceed in an upward slope and then to level out parallel to the bottom cover pa per. If the bottom cover paper were not suppo'. ted by the table or other support it also would be bulged downin thocoromaterial wardly. n will be apparent; at the extent that this action occurs, that a thicker board, that is, one a the desired thickness of the board.

I account for this action by what may be termed the hydraulic pressure which is created in the mass of the core material in plastic condition which is built up ahead of and bears against the top cover paper as it moves into contact with and around the upper forming roll. While the presence of this hydraulic pressure may not be fully explained, apparently it in part may be caused by the height. of the mass of plastic material producing a static head after the manner of a fluid tending to force theplastic material through the space between the top and the bottom cover papers at the point Just between the forming rolls. This plastic and somewhat fluid mass tends to seek its own level and to now from the accumu lated mass through the space between the form,-

ing rolls and to force the cover papers apart after the formed board. 'lhe present invention provides means and a process which accomplishes such counteraction to maintain a predetermined thickness of the board. The device of the invention also may be effective, however, for preventing' the wavy or uneven surface which it was the purpose oi the Turner patent'to overcome.

The invention will be more fully understood from the description of the drawing in which:

Fig. 1 shows a diagrammatic section longitudinally of a portion 01a wallboard machine embodying the device of the invention.

Fig. 2 is a cross section on line 2-2-of Fig. 1.

Fig. 3 is a diagrammatic longitudinal section 4 chine, a sheet of bottom cover paper 2 may be they leave the rolls. This hydraulic pressure action also in part may be accounted for by the mechanical pressure of the mass accumulated against the top cover paper as it moves around and in contact with the upper forming roll. This mechanical pressure is caused by the push of the mass of plastic material as it-is carried forward by the bottom cover paper. While other forces may enter to produce or to increase or modify what herein is called hydraulic pressure, it is my observation that the action which occurs, if not exactly or fully accounted for as above described. is such as to continually force a certain excess amount of the plastic material through the space between the two cover papers as they pass between the forming rolls and thus to increase the thickness of the board.

It is a principal object 01. the Present invention to overcome this action and to produce boards oi predetermined thickness.

It is also an object of the invention to produce products of this type which will be of greater uniformity of thickness than heretofore regardless of variations in the amountof materialbeing red to the machine and regardless of variations 4 inthe composition, consistency or other properties of 'such'materials' tending to create dinerences in the plastic condition, inthe weight of delivered upon a supporting table 3 and continuously moved across this-table in the direction of the length of the sheet of paper in the manner commonly practiced in the manufacture of gypsum wallboards. Above the table 3 and the paper 2 moving thereover, means 5 of conventional construction is arranged for delivering through discharge outlets the core material in plastic condition such as is provided in the case of gypsum wallboards by a slurry formed of calcined gypsum and water. The control of the consistency of this materialis'spread fairly evenly upon the cover paper 2. Over a period of time the amount is equal to that amount which is to be contained between the cover papers of the finished product which in the same time have been delivered to the machine from rolls such as the rolls l and H. i From the roll l suitably supported above the I table 3 the sheet II of top cover paper is delivwhat may be said to be in angular relation so'as to leave a space for the delivery means-5 for distributing the plastic material upon'the bottom materialhandled, and in the head or build-up of to the conveyor which carries the formed product tromtherormingroll. Noprovisionismadeinthe device of this patent; howeveaior preventing separation or the cover papers by the hydraulic pressure hereinabove described. there being .no means disclosed in thcpatent for backing up both cover papers as in the present invention to .re-

betweenthecovcrpapersof 1| cover paper. In the ordinary wallboard machine the top cover paper I! is fed around the bottom side of the upper forming roll' il,'as shown in Pig. 3, positioned above a lower forming roll 4 inserted in the table 3 and at such a distance therefrom that'the'top cover paper II after leaving .said' roll l3 and being then moved in the horizontal direction and generally parallel to the movementof thc bottom cover paper 2 becomes applied to the core material while spaced from the bottom paper 2 at a distance intended to determine the thickness oi the finished wallboard.

Inthe ordinarywallboardmachinetherollsl and' II are positively rotated or otherwise caused to rotate with the movement'of the cover papers 2 and l2,thetopcoverpapermovingcircumi'erentially in contact with the 'roll n; The'gen-.

eral location of the portion ll of the device 01 theinvention sbowninl'lg. 1 is thesame as that ofthe toproll l3 mm. 3. For the reasons which have been explained hereinabove such'a roll ll ordinarymachinetheupperforming rollllkinteadedtoservethemmnotonlyor positioning tbehorisontal stretch of the top coverpopcrlncontactwiththecoromateriat about because of the mechanical push or pressure of the mass 9 as it is carried forward by the bottom cover paper 2. Since the mass is in plastic condition and in some cases capable of flow, both this mechanical pressure as well as the hydraulic pressure due to the height of the mass greater than the thickness of the core between the cover sheets will transmit force hydraulically to the portion 16 which is moving between-the parallelly moving cover sheets 2 and I2. As has been described above, this pressure tends to separate these cover papers in the vertical direction in the ordinary machine, as may be understood from Fig. 3 where for purposes of illustration the lift of the top cover paper under the hydraulic pressure is shown to a somewhat exaggerated degree.

In place of the roll l3 in one embodiment a member !4 is used in the device of the invention. This member I4 preferably has a curved surface which may correspond to the circumference of the roll is and is positioned to receive delivery from the roll of paper II of the cover paper l2 so that this cover paper may be drawn around the curved surface of the member l4 into the horizontally extending direction. With its surface i! continuous with and preferably tangent to the curved surface of the member I4 is a plate portion l5 which,'if desired, may be a separate piece suitably fastened to the member l4. This bottom surface I! is formed as a plane surface in the horizontal plane parallel to-the horizontal plane surface i which may be an extension of the top surface'of the table 3. The portion 15, which may be in the form of a plate suitably braced and stiffened with ribs or other structural means to maintain the plane surface I! thereof against bending or other deformation, is held by suitable means, not shown, in fixed relation to the table 3 and its extension 8. The plate l5 and the curved member l4 connected therewith may be mounted if desired so as to be adjustable vertically in relation to the table 3 to provide for formation of boards of different thicknesses. On theother hand, the portion 8 of the table 3 which provides the surface! may be made integral with or as a part fixed in-relation to both the plate l5 and the member l4 so that these parts together may be removed from the machine as a whole and replaced when worn by others or by another device for producing a different thickness of the wallboard by virtue of greater spacing of the plate 8 and the plate l5 and its associated member l4. 1

The extension plate 8 of the table Land the extension of the plate l5 beyond the tangent point of the member N, that is, beyond the point at which the thickness of the board is determined,

"preferably is of substantial length in the direction of the movement of the board in order that for manufacture of ordinary gypsum wallboard the length of the plate I5 beyond th tangent point may be of the degree of 12 to 24 inches when using ordinary core forming materials of calcined gypsum. For the purposes of the invention such a length of travel of the formed board is used that sufllcient opportunity is given for the hydraulic forces acting upon the calcined gypsum or other plastic core materialdistributed' between the cover sheets to be counteracted or dissipated and for the cover sheets to be pressed into contact with the core. The spreading of the top and bottom cover papers which occurs in the conventional process and the increase of the amount of core material therebetween which produces the increase in thickness of the finished product thusis prevented. The length of the plates l5 and 8, however, may be increased or decreased depending upon the particular properties or qualities of the core material in its plastic condition before setting or hardening. The device of the invention is effective to determine the desiredthickness of the board by the fixed distance of the upper plate l5 from the lower plate 8 and without the necessity for adjusting the distance between these two plates as has been the practice when a cylindrical member such as a roll 13 was used.

In the manner provided for in the ordinary wallboard machine the formed product may be carried forward by a continuously moving conveyor 20 passing around ac'onveyor pulley 2| as the board is delivered from the forming device provided by the plate 8 and the plate i5 and its auxiliary member, l4. As with the ordinary wallboard machine, this conveyor carrying the formed product toward the cutter knife serves to draw the paper from the rolls I and II and to draw the plastic material from the mass 9 into the space between the cover papers.

In the modification of the apparatus of the invention as shown in Fig. 4, in' place of the plate l5 and its auxiliary'member Id of Fig. 1, a device constructed with an endless belt-or apron 25 is arranged so as to function in relation to the top cover paper 2 in a manner similar to the plate i5 and the auxiliary member M. For this purpose the endless belt 25 is carried by drums 2'! and 29. These drums may be respectively mounted upon shafts 3| and 33 supported in suitable bearings not shown. By means of any suitable belt tcnsioning mechanism the shaft 33 'may be moved relative to the shaft 3l-so as to maintain a substantial tension upon the belt or apron25. As 'will be apparent from Fig. 4, the top cover paper 2 is fed toward the bottom cover paper I in angular relation thereto and so as to circumferentially pass around the drum 2l but in contact with the belt 25 rather than directly with the drum 21. The shaft 3| or the shaft 33 or both may be suitably driven to cause the belt 25 to move in the direction of the arrows, that is, so as to move concomitantly with the movement of the paper 2 as it moves toward and then parallel to the cover paper I. The

I formed board which has been referred to above these plates may provide sufflcientarea for resistance to the hydraulicpressure which, as above described, tends to separate the two cover papers as they move horizontally from the forming dein the description in connection with Fig. l as requisite to dissipate the hydraulic pressure and to maintain the predetermined thickness of the board.

The belt or apron 25 may be made of any suitable material which is capable of being placed under substantial tension by the setting of the shafts II and 23. For the purpose of withstanding the stress thus brought upon this belt or apron it may be made of relatively thin flexible sheet steel which may be welded or otherwise formed in an endless belt. If the drums 21 and 29 are formed as true cylinders andwith their shafts 3| and 33 parallel and parallel to the plane of movement of the bottom cover sheet I,

the surface of the stretch 25 may be maintained in the parallel position by the tensionof the belt.

' As such a belt 25 must be suiliciently flexible -the bottom stretch 26 thereof, may be insuflicient to maintain this stretch 25 substantially in the plane parallel to the plane of movement of the bottom'cover sheet I. In other cases and 'with some plastic core materials this stretch need not be placed under great stress in order to make it taut. Wherever desired or' necessary this stretch 26 may be backed by a rigid plate 35 overthe bottom surface '36 of which the stretch 26 slides. This bottom surface of the plate 35 may be a smooth plane surface and the plate 35 may be set sopthat-the surface 36 is in the plane parallel to the bottom cover paper I and rigidly held in this position, thus to position the flexible stretch 26 of the belt bearing theron. It will be apparent that the pressure hydraulically acting throughthe portion I of the core material in the manner described above in connection with Figs. 1 and 3 willbe resisted and counteracted of formation of the board where the corema-j terial from the mass '9 is drawn between the- .may be such that they respectively are positioned ahead of and following the positions of the shafts 3| and 33 so that full support is obtained for the cover paper I and the core material carried thereby and to receive the counteracting'pressure or action of the belt and its backing plate 35 to prevent the separation of the two cover papers. In the above description the explanation of the action of the hydraulic pressure has been given in connection with the top and bottom cover papers. Whether the wallboards are of the type formed with closed edges, as mentioned hereinabove, or have openedges over which the cover paper is not folded, it is desirable or necessary that hopper sides 52 and 54 shown in Figs. 2 and 3 be used. In the ordinary wallboard machine these hopper sides are provided to prevent lateral flow of the mass of the plastic material 9 and to by the bottom stretch 26 of the belt '25 or by this stretch backed up by the plate 35.

The .above description of Fig. 4 is given as if the bottom cover paper I were supported upon a plane table such as the table 3 and its extention 8 of Fig. 1. The modification of Fig. 4, however, may include a belt or apron Ill stretched about drums l2 and 44 respectively carried by shafts 46 and 41 and'arranged with a tension ing'device in the manner suggested in connection with the shafts '3I and 33. It will be apparent that the upper stretch ll of the belt 40 may 'act in a similar manner with respect tothe .bottom cover paperJ as does the bottomstretch back up this flow and the cover paper when folded over at the longitudinal edges of thecoverv sheet. In such an ordinary wallboard machine the hopper sides 52 and 54 extend through the nip.

of the rolls 4 and I3 and to the extent of an inch or two or somewhat more beyond the nip of the core material being used. Where the form of the apparatus as illustrated in Fig. 4 is used the hopper sides also may be extended for the full length of the horizontal stretches 26 and M J respectively of the belts 25 and 40 or for such mass of core material 9 is transmitted through the portion I! of this core material to the cover papers I and 2.- The, belt III and its supporting drums maybe substituted for the portion 8 of Fig. l, which is the extension of the table 3, and may be of such; length as properly to carry the bottom cover paper and the core material until it is transferred to the conveyor belt 2II.

If necessary a plate 5. may be inserted between the belt 4' where it passes over the drumand; the conveyor 2| to bear the weight of the board until itbecomes carried by the conveyor 2|. It will be apparent that the belt I,

portion of such extent as will prevent bulging of the longitudinal edge surfaces of the wallboards where, in closed edge boards, they are covered by the folded over margin of the cover paper.

While the invention is shown in the drawing only in a diagrammatic form, it will be apparent, without departing from the invention, that variousarrangements of the parts may be made,

such as the supports for the rolls of cover papers I and I I and of the means'5 and 6 for delivering the core material to the space betweenthe cover papers. It is ordinarily desirable or necessary that the top cover paper I2 be delivered at an angle to the bottom cover paper 2 in order that that is, the distance between the shafts l5 and I1, 1

stantially less than the distance between the shafts II and 32' in order'that the full areas in contact respectively with the top cover paper 2- and the'bottom cover paper I, beyond the point suiiicient separation of the papers may be accomplished to introduce the plastic material therebetween. Any variation 0r modification of the arrangement of the parts, however, which meets the condition that a mass 9 of the core material in plastic condition delivered between the cover papers acts to create hydraulic pressure, as has been described, tending to force the plastic material through the restricting space between the member I! and timetable 3.0;- its bottom plate 8 and thereby to raise the top cover paper, is within the scope of the invention when means are utilized to counteract the force of this hydraulic pressure.

The invention makes possible not "only control of the thickness of the finished product as above describedv under a given set of manufacturing conditions as well as avoiding variations in thickness due to variations in the properties and qualities of the core'material while in the plastic 'condition but also makes possible better control of the auxiliary processes which are necessary in the manufacture of a wallboard product which utilizes an hydraulic setting material for the core- .between the cover papers.

In the manufacture of gypsum wallboards, for example, after they are formed and after the gypsum core has become set and following the cutting of the long length of board material into panels of definite length, it is necessary to dry the excess water from the core material. To do this for the most part the moisture to b evaporated must pass out through the cover sheets. For eflicient and effective removal of this moisture the boards are passed through a drying kiln maintained' at a temperature approximatelyin the range between 225, 52-350? F. If the boards are of greater thickness than the desired thickness,

as has been explained they will carry a larger amount of core material than is desired. The water in this excess core material must be evaporated and the drying operation must be continued for a longer time or must be carried on at a higher temperature in order to insure complete drying of the panels; This involves increase in the cost of manufacture. Where the time of passage through the removed. This may result in overheating of some panels in order to secure sufiicient dry g of all the panels. Where the panels become overheated calcination of the set core material, that kiln is limited or fixed, increase of. the heat is necessary if this'excess water is to be An additional advantage obtained by the invention in securing uniform thickness of formation of the wallboard is that when the panels is, driving off of the water of crystallization may occur, resulting in a powdery or friable core, particularly at the edges thereof.

It also will be apparent that where the boards are formed thicker than the predetermined thickness the excess of the core material which is forced between'the cover papers by the hydraulic pressure is wasted and the weight of th panels exceeds the desired weight. The loss occassioned by supplying excess material as well as the excess cost of transportation because of excess weightare avoided when in accordance with the invention the variation, that is the increase of thickness, is prevented. Where the thickness is controlled to the standard or. predetermined thickness the strength of the panels may be more exactly predetermined and the controls of the composition and condition of the slurry and other conditions-of the board forming operation necessary for securing strength, rigidity and other mechanical properties of the panels become much simplified.

made therefrom are erected in a building construction with the adjacent edges of adjacent panels meeting upon a common stud or other supporting structural member, the faces of the panels become flush with each other rather than in offset relation. This makes it possible to secure an even wall surface and one in which at each joint there is no difference in elevation of the two surfaces which-may become evident in a finished wall even though a suitable joint covering material is used.

While the embodiment of the invention as shown in Fig. 1 has the advantage of simplicity and no moving parts in the forming device requiring mechanical drive and adjustment, the embodiment of Fig. 4 has the advantage of avoiding possible damage to the top cover paper 2 in sliding over the surface of the members 14 and I5 of Fig. 1. Anyforeign material which may fall between the cover paper and the belt 25 is carried forward and may be removed as the belt 25 passes around the drum 29. This embodiment also places less stress upon the cover papers as the belts 25 and 40 move concomitantly with these cover papers.

Having thus described my invention I now claim:

1. In a machine for producing wallboard having a core of calcined gypsum in set condition between sheets of cover paper, a substantially horizontal sheet-supporting table, a plate fixed above and extending across said table and having one portion thereof parallel to said table and another portion curved upwardly from said table,

said table and plate, and means for supporting a roll of cover paper above said table and arranged to be fed as a sheet around and along thecurved and horizontal portions of said plate and in covering contact with said plastic'mixture.

2. The machine set forth in claim 1 in combination with means for preventing the spread or said mixture outwardly beyond the opposite side edges of said plate.

GILBERT A. HOGGA'II. 

